According to 3GPP (Third Generation Partnership Project), in a radio communication system corresponding to standardized LTE (Long Term Evolution), a radio base station eNB assigns a radio resource (resource block: RB) to a radio terminal UE in radio communication between the eNB and the UE (for example, refer to Non Patent Literature 1). The eNB appropriately changes the resource block that is assigned to the UE. For example, the eNB assigns a wideband resource block to UE that is a transmission destination of a large amount of data, or UE with a high communication priority.
Furthermore, in the radio communication system corresponding to the LTE, one of FDD (Frequency Division Duplex) and TDD (Time Division Duplex) is employed in the radio communication between the eNB and the UE.
Moreover, in an LTE (TDD-LTE) radio communication system employing the TDD, there has been discussed a feature where the eNB calculates an antenna weight according to a reception situation of a sounding reference signal (SRS) that is an uplink radio signal transmitted by the UE, and performs control (beamforming) for adaptively directing a beam toward UE of a transmission destination when transmitting a downlink radio signal or control (null steering) for directing a null toward UE other than the transmission destination, in order to ensure communication quality between the eNB and the UE that is moving.
Under an environment in which a resource block assigned to the UE is appropriately changed, in order to perform the beamforming or the null steering, a frequency band of a resource block to be assigned to the UE needs to be included in a frequency band of SRS. That is, the frequency band of the SRS also needs to be appropriately switched.
To this end, the eNB performs the following process. The eNB transmits, to the UE, an RRC (Radio Resource Control) Connection Reconfiguration message including a parameter related to the transmission content, transmission method and the like of the SRS. The UE transmits an RRC Connection Reconfiguration Complete message to the eNB as a response message, and switches and transmits the SRS according to the parameter. The eNB calculates an antenna weight according to the reception situation of the SRS.